Go to Shopify > Setting > Location
Click on the Shipping origin address
Tick on “Fulfill online orders from this location” checkbox. It has to be checked so the inventory can be sold.
Finally, click on Save.
I hope this might be helpful for you.
Should you have any other concern, feel free to let us know via our live chat channel by clicking on the bottom right icon inside app, or our email at email@example.com.